The invention pertains to methods of forming solids, and in particular applications pertains to methods of forming solids comprising tantalum and silicon. The invention also pertains to solids which comprise tantalum and silicon, and in particular applications pertains to sputtering targets and methods of forming sputtering targets.
An on-going trend in semiconductor processing is to incorporate copper into semiconductor devices. Copper can have advantages relative to other materials in that copper is exceptionally conductive. However, a difficulty in utilizing copper is that copper atoms can diffuse through a number of commonly-utilized materials. If copper atoms diffuse into materials that are intended to be insulative, the copper atoms can render an integrated circuit device unusable. Accordingly, there has been an effort to develop barrier layers which can prevent copper diffusion. Barrier layer materials which have received particular interest are materials comprising tantalum and silicon. Such materials can comprise a homogeneous mixture of tantalum and silicon, and can further comprise one or both of nitrogen and oxygen.
Materials comprising tantalum and silicon can be sputter-deposited from targets comprising the tantalum and silicon in a desired stoichiometric ratio. Typically, the targets will comprise at least about 70% tantalum, and the remainder will be either silicon, or a mixture of silicon with one or more other elements. If the sputter-deposition occurs in an atmosphere which is inert relative to reaction with the materials of the target (such as, for example, an argon atmosphere), a film having a composition approximately identical to that of the target will be sputter-deposited from the target. If the target is instead exposed to an atmosphere reactive with one or more materials of the target (such as, for example, an atmosphere comprising one or both of nitrogen and oxygen), a film can be deposited which has components from the atmosphere in addition to the components from the target material. For instance, if a target consisting essentially of tantalum and silicon is sputter-deposited in a nitrogen atmosphere, a film comprising tantalum, silicon and nitrogen can be formed. Further, if a film comprising tantalum and silicon is sputter-deposited in an atmosphere comprising oxygen, a film comprising tantalum, silicon and oxygen can be formed. Suitable sources of nitrogen can include, for example, N2; and suitable sources of oxygen can include, for example, O2.
Ideally, a sputtering target comprising tantalum and silicon will have a homogeneous mixture of tantalum and silicon throughout its construction so that homogeneous films will be formed from the target. However, it is found to be difficult to form targets having homogeneous distributions of tantalum and silicon. Specifically, a traditional method for forming a homogeneous mixture of solid materials would be to melt the materials together, and then solidify the melt into a solid comprising a homogeneous distribution of the materials. However, traditional technologies do not work with tantalum and silicon, and to date there has been no process developed which can form a homogeneous mixture of tantalum and silicon from a melt. Instead, the present technologies for attempting to form homogeneous solid mixtures of tantalum and silicon are to mix tantalum and silicon powders together, and thereafter subject the powders to compressive forces which mold the powders into a solid form. While such technologies can form solids which approach a homogeneous distribution of silicon and tantalum materials, there can be pockets within the materials wherein the tantalum and silicon powders were not uniformly distributed, and accordingly wherein the composition of the solid is not homogeneous relative to other portions of the solid. Accordingly, it would be desirable to develop new technologies for forming homogeneous mixtures of tantalum and silicon.
Although a motivation for the present invention was to develop a better process for forming homogeneous solid mixtures comprising tantalum and silicon, the invention is not limited to processes comprising tantalum and silicon. Accordingly, in one aspect the invention encompasses a method of forming a solid from at least two different powdered materials. A first and second of the different powder materials is compressed into a pellet. A melt pool is formed at a temperature which will melt both the first and second materials. The pellet is fed to the melt pool and the first and second materials are melted. The melted first and second materials are subsequently cooled to form the solid.
In another aspect, the invention encompasses a method of forming a solid which includes tantalum and silicon.
In yet another aspect, the invention encompasses a homogeneous solid comprising tantalum and silicon, and formed from a molten mixture of tantalum and silicon. For purposes of interpreting this disclosure and the claims that follow, a xe2x80x9chomogenous solid comprising tantalum and siliconxe2x80x9d refers to a solid in which the relative concentration of tantalum to silicon is constant throughout the composition of the solid.